The disclosure relates to an adjustable hydraulic pump according to the description below.
In adjustable hydraulic pumps, what is referred to as a zero stroke operating mode can lead to problems, in particular if said operating mode lasts for a relatively long time. This zero stroke operating mode occurs, for example, when a consumer which is supplied by the hydraulic pump is not to be operated for a relatively long time and in the process the hydraulic pump continues to be driven in a rotating fashion.
In order to ensure a minimum throughput of pressure medium in order to lubricate a hydraulic pump, it is known from the prior art to operate the hydraulic pump with a minimum stroke in order to deliver a minimum amount of pressure medium. This solution is subject to tolerances and is dependent on temperature and leakage.
Documents DE 198 50 611 C1 and DE 10 2008 038 435 A1 present an adjustable hydraulic pump in which the control pressure supply of the adjustment device can be provided, on the one hand, via a working line of the hydraulic pump, or, on the other hand, via a further “external” control pressure supply. The alternating connection to the respective control pressure source with a relatively high pressure is carried out here via a shuttle valve. A disadvantage of this solution is that the state of the shuttle valve is undefined when the pressure at its two inputs is equal. In this context, the shuttle valve can be closed and damaged. This can in turn lead to a failure of the adjustment device and to a failure of the hydraulic pump.